Flann is both an English surname and an Irish masculine given name, but has also been used as a feminine given name.^[1]

It might refer to:

• Flann Fína mac Ossu, another name for King Aldfrith of Northumbria (died 704 or 705)
• Flann mac Lonáin (died 896), Irish poet
• Flann Sinna (died 916), also called Flann mac Maíl Sechnaill, High King of Ireland
• Flann Mainistrech (died 1056), Irish scholar
• Flann O'Brien, a pen name used by Irish writer Brian O'Nolan (1911–1966)

FLANN, an acronym for Fast Library for Approximate Nearest Neighbors, is a C++ library for approximate nearest neighbor search in high-dimensional spaces.^[2]